Arginase activity and nitrogen content in epidermal carcinogenesis in mice.

This is one of a series of investigations the pur pose of which is to characterize the nitrogen metabolism of mouse epidermis in various phases of growth and in carcinogenesis. It was reported previously that mouse epidermis has high concen trations of urea and preformed ammonia (1) and considerable arginase activity (92).The purpose of this communication is to report data on arginase activity in the epidermis of mice undergoing car cinogenesis as a result of treatment with methyl cholanthrene in benzene and in control mice. These include animals treated with benzene alone or with a dilute solution of croton oil in benzene, a non-carcinogenic irritant. Finally correlative data on total nitrogen, trichloroacetic acid-soluble ni trogen (TCA-soluble N), urea, and preformed am fnonia contents will be presented. Reports in the literature give the general im pression that the arginase activity of malignant tissues is higher than that of normal tissues, and this has led to the suggestion that the in creased arginase activity may be associated with accelerated rates of protein synthesis and cell division (3, 4). Liver tumors, however, have much less arginase activity than the normal parent tis sue (5). Probably the chief function of arginase in the liver is to form urea from arginine as part of the ornithine cycle. However, the function of ar ginase in the extrahepatic tissues is not known. The presence of large quantities of urea and pre formed ammonia (1), and the detection of free ar ginine (6) and arginase activity (92) suggest the possibility that the ornithine cycle may also be operative in mouse epidermis. This is under in vestigation at the present time. It has been sug gested that arginase may participate in the trans fer of the amidine group of arginine to glycine to form guanidoacetic acid in the kidney (7). This enzyme may also be concerned with the metabo lism of the arginine-rich histones. None of the roles suggested for arginase in the cellular economy